Sintered cermet material for cutting tools and method for producing the same

ABSTRACT

Sintered cermet materials for tools such as cutting tools, which are excellent in heat resistance, wear resistance and fracture resistance, are inexpensive, and have long life time, and a method for producing such sintered cermet materials. The sintered cermet materials for tools are composed of sintered bodies which are obtained by preparing a mixed powder containing powders of TiCN, Si 3 N 4 , Al 2 O 3 , CrxN (x=1-2.7) and ZrN, at least one powder of W and WC, and at least one kind of metal powder selected from the group consisting of Co, Ni, Ta and Mo, and sintering the mixed powder.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a sintered cermet material whichcan be effectively used in tools for machining special work pieces, anda method for producing such cermet material. The sintered cermetmaterial of the present invention is in particular suited for machininghigh class cast iron such as niresist cast iron and austemperedspheroidal graphite cast iron, as well as norm cast irons includingspheroidal graphite cast iron and flaky graphite cast iron. The productsare especially adapted for an efficient machining at a high feedingrate. 2. Technical Background

[0003] The technical background will be explained with reference tocutting tools for machining high class cast iron such as niresist castiron and austempered spheroidal graphite cast iron. Niresist (Ni-Resist)cast iron is a nickel-chromium-copper austenitic cast iron, in whichgraphite is distributed in an austenite matrix. Niresist cast iron isexcellent in resistance against wear, heat and corrosion, in relation tonormal cast irons, and accordingly is widely used as a material forvarious machine part which are demanded both hot strength and wearresistance as employed in corrosive circumstances. In particular, recentremarkable improvements in automotive has made performance of motorvehicles have made niresist cast iron principal material for the primaryparts of motor vehicles. On the other hand, m an austempered spheroidalgraphite cast iron, which is obtained by heat-treating spheroidalgraphite cast iron, graphite particles exist in bainite and austenitephases. For this type of cast iron reference is made to JIS G 5503 FCAD1000-5. Austempered spheroidal graphite, with such high tensile strengthand excellent wear resistance over common cast irons, has become apromising material for mechanical parts to be used in aggressivecircumstances. It surely is going to be a good material for theconstruction of motor vehicles, which are now under pressure ofreduction in body size and weight.

[0004] In order to shape high class cast iron such as these niresistcast iron and austempered spheroidal graphite cast iron into finalconfigurations and dimensions of the basic important parts, normally,the high class cast iron has been frequently required to be subjected toa cutting work after cast. Cutting tools for cutting high class castiron such as these niresist cast iron and austempered spheroidalgraphite cast iron must have the performance that such high class castiron can be cut rapidly with a required cutting accuracy without waste.If tip ends of cutting tools are worn out or filed upon chipping or likeoperations, there occur folding and burr in cut surfaces of high classcast iron such as these niresist cast iron and austempered spheroidalgraphite cast iron, and consequently required dimensional accuracy andsurface roughness cannot be obtained, resulting in products that cannotbe shipped.

[0005] For these reasons, when the tip ends of the cutting tools areworn out or fractured, the cutting tools must be immediately replaced.The replacement of cutting tools decreases the productivity. Therefore,the number of replacements must be reduced to its minimum. For isreason, the development of cutting tools that have long tool life andare inexpensive has been earnestly demanded. TiCN sintered cermetmaterials disclosed in publications of Japanese unexamined patentapplications Nos. Sho 62-280362 and Sho 62-278265, for example, havebeen proposed as materials for cutting tools capable of overcoming theseproblems.

[0006] High class cast iron such as these niresist cast iron andaustempered spheroidal graphite cast iron (hereinafter referred to asADI) exhibits high hardness, and is excellent in wear resistance, ascompared with normal spheroidal graphite cast iron, and in ADI, theaustenite structure is transformed to martensite due to stress generatedupon cutting the work, and consequently the hardness of the structureitself increases remarkably during the cutting work. In addition, suchhigh class cast iron generates heat vigorously during the cutting work,as compared with the case of normal spheroidal graphite cast iron.Furthermore, where the high class cast iron castings have a roughenedas-cast surface, which needs to be cut first. Upon cutting these coarsecasting surfaces, interrupted cuts which cause vibration may occur.Accordingly, cutting tools have been required to exhibit toughnessendurable against these interrupted cuts.

[0007] As described above, the cutting tools for machining high classcast iron are required to have a wear resistance adequate for the hardhigh class cast iron, heat resistance causing no thermal degradation(decrease in hardness) due to heat upon cutting, and toughness (fractureresistance) enduring the interrupted cuts which occur upon cuttingcasting surfaces. The TiCN sintered cermet materials disclosed in theabove-described publications, however, are particularly low in heatresistance so that the hardness thereof decreases due to heat uponcutting, and consequently the wear resistance is decreased. This resultsin that the cutting tools must be replaced frequently.

[0008] In order to improve only the wear resistance (hardness) cuttingtools, each containing cBN and diamond, may be used. These cuttingtools, however, are low in toughness, and consequently, may be fracturedduring cutting works.

[0009] As described above, conventionally, there have been used nocutting tools exhibiting the wear resistance, heat resistance andfracture resistance, which are all required to cut high class cast ironsuch as niresist cast iron and austempered spheroidal graphite castiron, and accordingly the extension of the tool life, which has beendesired as cutting tools, has not been able to be effected.

SUMMARY OF THE INVENTION

[0010] It is one object of the present invention to provide sinteredcermet materials capable of composing inexpensive tools such as cuttingtools, which exhibit excellent heat resistance, wear resistance andfracture resistance, and have long life time, and a method for producingsuch sintered cermet materials.

[0011] It is another object of the present invention to provide sinteredcermet materials capable of composing inexpensive cutting tools, eachhaving long tool life, which can cut metal work pieces composed of notonly normal cast iron such as spheroidal graphite cast iron and flakegraphite cast iron but also high class cast iron such as niresist castiron and austempered spheroidal graphite cast iron, inclusive of castingsurfaces thereof, under severe conditions such as a high speed cutting,heavy cutting, and interrupted cutting, and a method for producing suchsintered cermet materials, especially where the present invention isapplied to cutting tools as typical tools.

[0012] The present inventors have continued to develop sintered cermetmaterials for cutting tools and a method for producing such sinteredcermet materials over many years. As a result they have found that bypreparing a mixed powder containing powders of TiCN, Si₃N₄, Al₂O₃, CrxN(x=1-2.7) and ZrN, at least one powder of W and WC, and at least onemetal powder selected from the group consisting Co, Ni, Ta and Mo, andby sintering the prepared mixed powder, the above-described objects canbe achieved, and, based on this finding, they have completed the presentinvention.

[0013] The reason why the above-described objects can be achieved hasnot been sufficiently clarified, but can be estimated as follows: Bypreparing a mixed powder containing powders of TiCN, Si₃N₄, Al₂O₃, CrxN(x=1-2.7) and ZrN, at least one powder of W and WC, and at least onemetal powder selected from the group consisting of Co, Ni, Ta and Mo,and sintering the prepared mixed powder to compose a sintered cermetmaterial, the crystal structure has a structure varied from TiCN, Si₃N₄,Al₂O₃, CrxN (x=1-2.7) as starting raw materials, and this new phasecontributes to the improvement of the quality of the material uponcutting or other operations. Where the sintered cermet material iscomposed by sintering another mixture material which is similar to theabove-described mixture material but does not include CrxN, such newphase does not appear, and sufficient heat resistance, wear resistance,future resistance or the like are not always obtained.

[0014] The sintered cermet material in accordance with a first aspect ofthe present invention is characterized in that the sintered cermetmaterial is composed of a sintered body which is obtained by preparing amixed powder containing powders of TiCN, Si₃N₄, Al₂O₃, CrxN (x=1-2.7)and ZrN, at least one powder of W and WC, and at least one metal powderselected from the group consisting of Co, Ni, Ta and Mo, and bysintering the prepared mixed powder,

[0015] The method for producing sintered cermet materials in accordancewith a second aspect of the present invention is characterized in thatthe method includes: the steps of preparing a mixed powder containingpowders of TiCN, Si₃N₄, Al₂O₃, CrxN (x=1-2.7) and ZrN, at least onepowder of W and WC, and at least one metal powder selected from thegroup consisting of Co, Ni, Ta and Mo, and sintering the prepared nixedpowder to obtain a sintered body.

[0016] The most noticeable point in the present invention is that bysintering using TiCN, Si₃N₄, M₂O₃, CrxN (x=1-2.7) and ZrN, the crystalstructure has a structure varied from starting raw materials composingthe mixed powder is recognized. It is estimated that by virtue of thesematerials, the heat resistance of tools such as cutting tools isimproved, the hardness and the strength in an elevated temperatureregion is ensured, the wear resistance and the fracture resistance areimproved, and the extension of tool life can be effected.

[0017] Therefore, where the sintered cermet material of the presentinvention is applied to the cutting tool as a representative tool, thesintered cermet material for cutting tools which can cut work piecescomposed of materials, each being difficult to be cut, such as highclass cast iron including niresist cast iron and austempered spheroidalgraphite cast, at high speed and intermittently, can be obtained. WithMe present invention, there can be obtained cutting tools which exhibitexcellent wear resistance and toughness under conditions such as a highspeed cutting, and have long tool life even where an intermittentcutting is performed, as compared with the conventional sintered cermetmaterials.

[0018] In order that the mixed powder enables the achievement of theabove-described functions, it is preferable that the mixed powdercontains 1 to 20 vol % of TiCN, 1 to 10 vol. % of Si₃N₄, 1 to 20 vol. %of Al₂O₃, 5 to 15 vol. % of CrxN (x=1-2.7) and 5 to 15 vol. % of ZrNsuch that the total of powders of TiCN, Si₃N₄, Al₂O₃, CrxN and ZrNranges from 13 to 70 vol. %, and the mixed powder further contains 20 to70 vol. % of at least one of W and WC, and 1 to 20 vol. % of at leastone selected from the group consisting of Co, Ni) Ta and Mo. Where suchmixed powder is sintered, the resulting sintered cermet materials have adifferent crystal structure from that of TiCN, Si₃N₄, Al₂O₃, CrxN(x=1-2.7) and ZrN, and by virue of strong bonding of these materials,excellent sintered cermet materials having long service life, which cancut work pieces, each being composed of materials difficult to be cut,such as high class cast iron including niresist cast iron andaustempered spheroidal graphite cast, at high speed and intermittently,can be obtained.

[0019] TiCN, titanium carbonitride, is formed with a continuous solidsolution of TiN and TiC, each having a cubic system. The atomic numberratio of N and C may range from (1:9) to (9:1). In order to obtaincharacteristics of both TCN and TiC favorably, the range from (2:8) to(8:2) is preferable. Where the amount of TiCN is too small, it isdifficult to act as the raw material of the sintered cermet material inaccordance with the present invention. On the other hand, where theamount of TiCN is excess, the balance with other starting materials suchas Si₃N₄, Al₂O₃, CrxN (x=1-2.7) and ZrN is difficult to be kept, andaccordingly, it is difficult to obtain a desired mixed powder.Accordingly, the preferred composition ratio of TiCN ranges from 1 to 20vol. %, and more preferably ranges from 5 to 20 vol. %. In accordancewith demand, 18%, 16% and 14%, for example, can be adopted as the upperlimit of the composition ratio of TiCN, and 6%, 8% and 10%, for example,can be adopted as the lower limit thereof.

[0020] It is preferable that the particle size of TiCN powder is small.Where the particle size of TiCN powder exceeds 10 μm, new materialsresulting from the above-described composition are not formedsufficiently. Under some sintering conditions, TiCN may excessivelyremain after sintered. In addition, even if all TiCN reacts and desiredmaterials am formed, it may occur the problem that the formed materialssegregate and do not disperse homogeneously. Accordingly, it ispreferable that the particle size of TiCN is 5 μm or less and, morepreferably, 2 μm to 1 μm or less. In general, super fine particles, eachhaying a particle size of 0.1 μm or less, are preferable. In this case,it is necessary to consider the removal of gas adsorbed in such finepowders.

[0021] It is preferable that the TiCN raw material for use in thepresent invention is a compound of a solid solution. Otherwise, acompact mixture of TiC and TiN can be used. For example, by usingmechanical alloying method of mixing and pulverizing TiC powder and TiNpowder, each being weighed to have a predetermined ratio, and having aparticle size of several micron or less, to obtain powders having sizesof submicron, a sintered material to the solid solution can be obtained.

[0022] Examples of the pulverizing device used in this case includegeneral purpose devices such as ball mills, vibration mills, planetarymills. Upon pulverizing, in order to prevent intrusion of componentsother than the composition materials of the present invention, balls,each being made of cermet which has substantially the same quality asthat of the composition of the present invention, are used Otherwise,balls, each being made of alumina or cemented carbide as one componentof the material of the present invention, are suitable.

[0023] Si₃N₄ has hexagonal system alpha-type and trigonal system β typein the crystal structure thereof Basically, any type of the crystalstructure is applicable. It is considered that the hexagonal systemalpha-type which is easy to dissolve oxygen in a solid state ispreferable. Where the amount of Si₃N₄ is too small, it is difficult toact as the raw material of the sintered cermet material in accordancewith the present invention. On the other hand, where the amount of Si₃N₄is in excess, the balance with other starting materials such as TiCN,Al₂O₃, CrxN (x=1-2.7) and ZrN is difficult to be kept, and it isdifficult to obtain a desired mixed powder. Accordingly, the preferredcomposition ratio of Si₃N₄ ranges from 1 to 10 vol,% and, morepreferably, from 5 to 10 vol. %. In accordance with demand, 9%, 8% and7%, for example, can be adopted as the upper limit of the compositionratio of Si₃N₄, and 3%, 4% and 6%, for example, can be adopted as thelower limit thereof. It is preferable that the particle size of Si₃N₄powder is small. Where the particle size of Si₃N₄ powder exceeds 10 μm,new materials to be resulted from the above described composition arenot formed sufficiently. Under some sintering conditions, Si₃N₄ mayexcessively remain after sintered In addition, even if all Si₃N₄ reactsand desired materials are formed, it may occur the problem that theformed materials segregate and do not disperse homogeneously.Accordingly, although sufficient attention should be paid to pollutioncaused by impurities, it is preferable that the particle size of Si₃N₄is 5 μm or less and, more preferably, 2 μm to 1 μm or less. In general,super fine particles, each having a particle size of 0.1 μm or less, arepreferable. In this case, it is necessary to consider the removal of gasadsorbed in such fine powders.

[0024] There are many types of crystal structures in Al₂O₃. Basically,the crystal structure thereof is not limited specifically, but S type ofthe cubic system spinel type which changes to alpha-type at 1000° C. ormore, arid S type of the trigonal system corundum type which is stableat high temperatures are preferable. Where the amount of Al₂O₃ is toosmall, it is difficult to act as the raw material of the sintered cermetmaterial in accordance with the present invention. On the other hand,where the amount of Al₂O₃ is in excess, the balance wit other startingmaterials such as TiCN, Si₃N₄, CrxN (x=1-2.7) and ZrN is difficult to bekept, and it is difficult to obtain a desired mixed powder. Accordingly,the preferred composition ratio of Al₂O₃ ranges from 1 to 20 vol. % and,more preferably, ranges from 5 to 20 vol. % to ensure favorableproperties. In accordance with demand, 19%, is % and 17%, for example,can be adopted as the upper limit of the composition ratio of Al₂O₃, and6%, 8% and 10%, for example, can be adopted as the lower limit thereof.It is preferable that the particle size of Al₂O₃ powder is small. M₂%powder of a high purity, each having the particle size of 1 μm or less,can be easily obtained, and accordingly such A1 ₂O₃ powder may be used.In this case, problems such as insufficient reaction and segregationwhich have been encountered with the case of TiCN, Si₃N₄ or the like cmbe restrained. In general, it is preferable that Al₂O₃ powder is superfine particles of which the particle size is 0.1 μm or less. In thiscases it is necessary to consider the removal of gas adsorbed in suchfine powders.

[0025] In CrxN (x=1-2.7) which is chromium nitride, CrN and Cr2N mainlyexist. These materials are both non-stoichiometric compounds. Where thecomposition ratio of CrxN (x=1-2.7) is less than 5%, it is difficult toact as a starting raw material of the sintered cermet material inaccordance with the present invention On the other hand, where thecomposition ratio of Cr×N is in excess, the balance with TiCN, Si₃N₄Al₂O₃ and ZrN as other starting materials is difficult to be kept, andit is difficult to obtain a desired mixed powder Accordingly, thepreferred composition ratio of CrxN (x=1-2.7) ranges from 5 to 15 vol. %and, more preferably, ranges from to 13 vol. %. In accordance withdemand, 14%, 13% and 12%, for example, can be adopted as the upper limitof the composition ratio of CrxN, and 6%, 7% and 8%, for example, can beadopted as the lower limit thereof. It is preferable that the particlesize of CrxN (x=1-2.7) powder is small. Where the particle size of CrxN(x=1-2.7) powder exceeds 10 μm, desired materials are not formedsufficiently. Under some sintering conditions, CrxN (x=1-2.7) mayexcessively remain after sintered Even if all CrxN (x=1-2.7) reacts anddesired materials are formed, it may occur the problem that the formedmaterials segregate and do not disperse homogeneously. Accordingly,although sufficient attention should be paid to pollution caused byimpurities where the particle size is small, it is preferable that theparticle size of CrxN (x=1-2.7) is 5 μm or less, and more preferably 2μm to 1 μm or less. In general, super fine particles, each having aparticle size of 0.1 μm or less, are preferable. In this case, it isnecessary to consider the removal of gas adsorb in such fine powders.

[0026] ZrN which is zirconium nitride exhibits high hardness and hightoughness at elevated temperatures, and where ZrN is used as thematerial of cutting tools, it is favorable for reducing the wettingproperty with work pieces. Where the amount of ZN is too small, it isdifficult to act as the raw material of the sintered cermet material inaccordance with the present invention. on the other hand, where theamount of ZrN is in excess, the balance with other starting materialssuch as TiCN, Si₃N₄, Al₂O₃ is difficult to be kept, and it is difficultto obtain a desired mixed powder. Accordingly, the preferred compositionratio of ZrN ranges from 5 to 15 vol. % and, more preferably, from S to13 vol. %. In accordance with demand, 14%, 13% and 12%, for example, canbe adopted as the upper limit of the composition ratio of ZrN, and 6%,7% and $ %, for example, can be adopted as the lower limit thereof. Itis preferable that the particle size of ZrN powder is small. Where theparticle size of ZrN powder exceeds 10 μm, desired materials to beresulted from the above composition are not formed sufficiently. Undersome sintering conditions, ZrN may remain after sintered Even if all ZrNreacts and desired materials are formed, it may occur the problem thatthe formed materials segregate and do not disperse homogeneously.Accordingly, although sufficient attention should be paid to pollutioncaused by impurities where the particle size is small, it is preferabletat the particle size of ZrN is 5 μm or less and, more preferably, 2 μmto 1 μm or less. In general, super fine particles, each having aparticle size of 0.1 μm or less, are preferable. In this case, it isnecessary to consider the removal of gas adsorbed in such fine powders.

[0027] With the present invention, in order to obtain good sinteredcermet materials, it is preferable that the mixed powder containspowders of. TICN, Si₃N₄, Al₂O₃, CrxN and ZrN such that the compositionratio of the total thereof ranges from 13% to 70 vol. %.

[0028] Tungsten which is W is added as a metallic component for ensuringthe toughness, or added to form tungsten carbide. W is the cubic system,and the alpha-phase of the body-centered cubic lattice thereof isstable. Basically, the crystal structure thereof is not limitedspecifically, but alpha-type which is a stable system is preferable. Onthe other hand, WC as tungsten carbide includes two kinds of alpha-type(hexagonal system crystal) and β type (cubic system crystal. Basically,the crystal structure thereof is not limited specifically. At least oneof powders of W and WC is contained in the mixed powder. In this case,the mixed powder may contain only W, only WC, or both W and W. When thecomposition ratio of W and WC in the mixed powder is less than 20%, itis difficult to act as the raw material of the sintered cermet materialin accordance with the present invention. On the other hand, where thecomposition ratio of W and WC in the mixed powder exceeds 70%, thebalance with other starting materials such as TiCN, Si₃N₄, CrxN(x=1-2.7), ZrN, Co, Ni, Ta and Mo is difficult to be kept, and it isdifficult to obtain a desired mixed powder. Accordingly it is difficultto obtain a desired sintered material. Therefore, the preferredcomposition ratio of at least one powder of W and WC in the mixed powderranges from 20 to 70 vol. % and, more preferably, from 30 to 60 vol. %.In accordance with demand, 65%, 55% and 45%, for example, can be adoptedas the upper limit of the composition ratio of at least one powder of Wand WC, and 23%, 25% and 30%, for example, can be adopted as the lowerlimit thereof

[0029] It is preferable that the particle size of at least one powder ofW and WC is small. At least one powder of W and WC of a high purity,each having a particle size of 1 μm or less, can be easily obtained andaccordingly such Al₂O₃ powder may be used. In this case, it ispreferable for reducing problems such as insufficient reaction andsegregation which have been encountered with the case of TiCN, Si₃N₄ orthe like. In general, it is preferable that at least one powder of W andWC is composed of super fine particles of which the particle size is 0.1μm or less. In this case, it is necessary to consider the removal of gasabsorb in, such fine powders.

[0030] With respect to Co, Ni, Ta and Mo as metallic components otherthan W, basically, the crystal structure thereof is not limitedspecifically. One kind of Co, Ni, Ta and MO may be contained, or twokinds or more thereof may be contained

[0031] When the composition ratio of the above described metalliccomponents in the mixed powder is too small, it is difficult to act astile raw materials of the sintered cermet material in accordance withthe present invention. On the other hand, where the composition ratio ofthe above-described metallic components in the mixed powder is inexcess, the balance with other starting materials such as TiCN, Si₃N₄,CrxN (x=1-2.7), ZrN, W and WC is difficult to be kept and it isdifficult to obtain a desired sintered cermet material. Accordingly, thepreferred composition ratio of at least one kind of metallic powders ofCo, Ni, Ta and Mo ranges from 1 to 20 vol. % and, more preferably, from5 to 15 vol. %. 18%, 17% and 16%, for example, can be adopted as theupper limit of the composition ratio of at least one powder of Co, Ni,Ta and Mo, and 3%, 4% and 5%, for example, can be adopted as the lowerlimit thereof. It is preferable that the particle size of at least onepowder of Co, Ni, Ta and Mo is small. At least one powder of Co, Ni, Taand Mo of high purity, each having a particle size of 1 μm or less, canbe easily obtained, and accordingly such fine powder may be used. Inthis case, it is preferable for reducing problems such as insufficientreaction and segregaon, which have been encountered with the case ofTiCN, Si₃N₄ or the like. In general, super fine particles, each having aparticle size of 0.1 μm or less is preferable. In this case, it isnecessary to consider the removal of gas adsorbed in such fine powders.The sintering temperature can range from 1300 to 1650° C. and, morepreferably, from 1350 to 1600° C. And the sintering pressure can rangefrom 0.1 to 3000 MPa and, more preferably, from 0.1 to 2000 MPa.

[0032] Hereinafter the operational advantages of the present inventionwill be explained

[0033] With the present invention, by preparing a mixed powdercontaining powders of TiCN, Si₃N₄, Al₂O₃, CrXN (x=1-2.7), ZrN, and W (Wonly, WC only, or both W and WC), each having the above-describedspecific composition ratio, and powders of at least one kind of metalpowder selected film the group consisting of Co, Ni, Ta and Mo, andsintering the prepared mixed powder, sintered cermet materials areobtained The sintered cermet materials which are formed by sintering themixed powder composed of these starting raw materials are excellent inheat resistance, and accordingly, where used in an environment in whichthe temperature is high, as tips of cutting tools, or the like, thehardness and strength thereof can be ensured, the durability isimproved, and the tool life can be extended. Accordingly, where thesintered cermet materials of the present invention are used as toolssuch as cutting tools, excellent durability and fracture resistance canbe achieved

[0034] Conventionally, where work pieces which are difficult to be cut,such as niresist cast iron and austempered spheroidal graphite cast ironwhich are called high class cast iron, are ocu even the sinteredmaterials of TiC, TiN or TiCN with Al₂O₃ have not been able to achievesufficient durability, It is considered tat this problem is caused bythe heat resistance, oxidation resistance and durability of the startingraw materials themselves being low. In contrast, with the presentinvention, by using the mixed powder which contains TiCN, Si₃N₄, Al₂O₃,CrxN (x=1-2.7), ZrN or the like in a specific composition ratio, as astarting raw Materials, in the obtained cermet materials, there areformed new crystal phases of which the crystal structure is changedrelative to that of TiCN, Si₃N₄, Al₂O₃, CrxN (x=1-2.7), ZrN.Accordingly, the obtained sintered cermet materials have very highhardness and excellent oxidation resistance, and these crystal phasesare bonded strongly. For these reasons, it can be estimated that theobtained sintered cermet materials are excellent in heat resistance anddurability.

[0035] Therefore, the sintered cermet material of the present inventionexhibits excellent beat resistance, oxidation resistance or durability,and accordingly is effectively applied to cutting tools, for example.Where the sintered cermet material of the present invention is used asthe cutting tools for cutting high class cast iron such as niresist castiron and austempered spheroidal graphite cast, vigorous shock and heatare generated in tips of tools. Since the sintered cermet material ofthe present invention has improved heat resistance and oxidationresistance, the wear resistance (durability) is ensured withoutdecreasing the hardness due to heat. In addition, since in the sinteredcermet materials of the present invention, newly formed crystal phasesare bonded strongly, the toughness is high, and fracture of cuttingtools can be restrained upon a heavy cutting and interrupted cutting,and accordingly cutting tools which are excellent in fracture resistanceand we resistance can be obtained.

[0036] In addition, with the present invention, it is preferable that 5to 20 vol. % of SiC is added with external addition to the mixed powderhaving the above-described composition, according to the quality of thematerial of the work pieces or the like. The method of adding 20 vol. %of SiC with external addition means the method t where the volume of themixed powder is 100, 20 of SiC is added to 100 of the mixed powder toobtain 120 in total. By adding SiC, the wear resistance of tools such ascutting tools is much improved. Examples of the upper limit of theexternal addition of SiC include 18%, 16% and 14%, and examples of thelower limit of the external addition of SiC include 6%, 8% and 10%.

[0037] SiC has two types of the crystal structure, namely alpha-type ofthe rhombohedral wurtzite type, and β type of the cubic systemzinc-blende type. Any type of SiC will do, but more elastic alpha-typeis preferable. By adding SiC, the hardness of the sintered materials isenhanced and accordingly the wear resistance of the obtained sinteredcermet materials is much improved. Where the amount of SiC is less tan $vol. %, the hardness is scarcely improved, and where the amount of SiCexceeds 20 vol. %, the balance in the above described composition isdifficult to be kept. In particular, the toughness of the matrix of thesintered cermet materials decreases, and accordingly, occurrence offractures inversely increases. In consideration of these problems, thepreferred amount of SiC to be added with external addition is determinedto range from 7 to 15 vol. %. It is preferable that the particle size ofSiC powder is smaller than that of the mixed powder. Where SiC powdermust be pulverized to disperse SiC as a reinforcement in a matrixhomogeneously, although attention should be paid to pollution byimpurities, it is preferable that the particle size of SiC powder is 3μm or less and, more preferably, 2 μm to 1 μm or less. In general, it isfavorable that SiC powder is super fine particles, each having aparticle size of 0.1 μm or less. In this case, it is preferable toconsider the removal of gas adsorbed in such fine powders. Where thewear resistance or other properties of the sintered cermet material issufficiently obtained without adding SiC, SiC may not be added.

[0038] The heating conditions upon sintering cal be 1300-1650° C.,preferably 1400-1550° C. The pressure upon sintering can be 0.1-3000MPa, preferably 0.1-2000 MPa.

[0039] Other objects, features, and characteristics of the presentinvention will become apparent upon consideration of the followingdescription and the appended claims with reference to the accompanyingdrawings, all of which form a part of this specification

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 illustrates an X-ray diffraction diagram showing the stateof each of a starting raw material and a resulting sintered material;and

[0041]FIG. 2 illustrates a perspective view illustrating arepresentative configuration of a cutting tool to which the presentinvention is applied.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS

[0042] Hereinafter, embodiments of the present invention will beexplained.

[0043] As sing raw materials, Si₃N₄ powder (silicon nitride) having anaverage particle size of 2.0 μm, TiCN powder (carbon titanium nitride)having an average particle size of 2.0 μm or less, Al₂O₃ (alumina)having an average particle size, of 1.0 μm or less, CrxN (chromiumnitride) having an average particle size of 2.0 μm or less, ZrN(zioninum nitride) having an average particle size of 2.0 μm or less andSiC (silicon nitride) having an average particle size of 2.0 μm or lesswere used. In addition tungsten powder having an average particle sizeof 2.0 μm or less and metal powder having an average particle size of2.0 μm or less were used. In the later described No. 6, a mixture of Wpowder (tungsten) and WC powder (tungsten carbide) were used as thetungsten powder, and in Nos. 1 to 9, and comparative examples 1 to 3, WCpowder was used as the tungsten powder.

[0044] As the metal powder, as shown in ( ) of the column M*4 of Table1, one kind of metal selected from the group consisting of Ni powder, Copowder, Ta powder and Mo powder was used. For restraining the formationof intermetallic compounds, only one kind of metal was used.

[0045] These powders were combined in the composition ratios shown inTABLE 1, and mixed together with a planet ball mill for 1 hour to obtainmixed powder s. Then, the mixed powder s were dried andcompression-molded with a mold to form molded bodies. As shown in thecolumn “pressure” of TABLE 1, the resultant molded bodies were held in apressurized state by a hot pressing or hot isostatic pressing (LW), orwith a piston•cylinder device, and then sintered The pressing conditionsupon sintering were as follows: pressure: 0.1 MPa-2000 MPa, temperature;1400 to 1550° C. and holding time: 0.5 to 6 hours. The concreteconditions of each test pieces are shown in TABLE 1. If the sintering iscarried out under a high pressure, the production costs increase.

[0046] Therefore, where good wear resistance is obtained by adjustingthe composition ratio of the mixed powder, the pressure while sinteringis determined so as not to increase highly.

[0047] After sintered, the temperature was decree and the pressure islowered to ob materials for cutting tools as test pieces No. 1 to No. 9which correspond to embodiments of the present invention. Thesematerials (No. 1 to No. 9) do not contain expensive cBN.

[0048] In the column “pressure” in TABLE 1, “*1” means that the hotpressing was carried out while flowing argon gas, “*2” means that thehot isostatic pressing (HP) was carried out, and *3 means thepiston•cylinder method of pressing work pieces, inserted into cylinderswith pistons. TABLE 1 Vol % Composition ratio (vol %) SiC Sinteringcondition Result of cutting test Embodiment WC, External PressureTemperature Time Wear Amount No. TiCN Si₃N₄ Al₂O₃ Cr₂N ZrN W + WC M *4addition (MPa) (° C.) (hrs) V_(B) (mm) 1 7 10 15 8 5 35 20 (Mo) 7   0.051550 2.5 0.192 2 10 7 18 10 5 40 10 (Mo) 0   0.10 1500 3 0.211 3 10 8 107 10 45 10 (Ta) 5  150 *2 1500 4 0.178 4 15 5 17 8 8 42  5 (Ni) 5  10 *11500 3.5 0.175 5 13 5 13 8 12 41  8 (Co) 7  10 *1 1500 4.0 0.168 6 20 1020 5 10 30  5 (Co) 20   0.1 1500 1.5 0.184 7 15 7 19 10 4 30 15 (Co) 7  0.05 1550 2 0.201 8 8 7 8 10 14 50  3 (Ni) 10   0.1 1450 4 0.189 9 135 13 12 8 34 15 (Ta) 7 2000 *3 1400 0.5 0.160 Comparative 30 0 30 5 5 2010 (Mo) 7   0.05 1550 1 0.244 Example 1 Comparative 40 1 30 0 15 12  2(Co) 2  30 *1 1800 2 fracture Example 2 Comparative 5 5 5 15 30 40  0(−) 0   0.1 1450 3 0.230 Example 3 Conventional cermet tool on themarket TiN—TiC—WC—Co — — — 0.542 Example 1 Conventional cermet tool onthe market TiCN—WC—Co—VC—MoC — — — 0.382 Example 2 Conventional cBN toolon the market cBN 80 vol %/(WC—Co) 20 vol % — — — fracture Example 3Conventional cBN tool on the market cBN 60 vol %/(Al₂O₃—TiC) 40 vol % —— — fracture Example 4

[0049] Peaks of the X-ray diffraction of the typical material forcutting tools (No. 5), which is one of the test pieces obtained by theabove-described method, are shown in FIG. 1. And, for comparison, peaksof the X-ray diffraction of the mixed powder before sintered are alsoshown. In FIG. 1,  indicates WC, ∘ indicates Al₂O₃, □ indicates TiCN, ⊚indicates SiC, Δ indicates ZrN, ▴ indicates Si₃N₄, ∇ indicates CrN, ▪indicates Co, and ? indicates unknown material,

[0050] As is apparent from the result of X-ray diffraction, which isshown in FIG. 1, it was confirmed that in the sintered cermet materialafter sintered, in accordance with the present invention, there wasformed a new material (which is a peak indicated by the symbol ? in FIG.1), of which the crystal mature is changed relative to that of TiCN,Si₃N₄, Al₂O₃, CrxN (x=1-2.7), ZrN and SiC as the sting raw materials.This new material is now unknown.

[0051] The materials for cutting tools, which had been respectivelyformed with the above-described method, were respectively shaped toobtain cutting tools, each having a prescribed configuration (JIS: SPGN120304SN). As shown in FIG. 2, the cutting tool has a triangularconfiguration having rounded comers. This cutting tool is entirelycomposed of sintered cermet material in accordance with the presentinvention Work pieces were cut using obtained cutting tools under thefollowing cutting conditions.

[0052] Cutting conditions

[0053] work piece: niresist cast iron having an external diameter of φ110 mm (JIS: FCA-NiCuCrl562 hardness: Hv163)

[0054] cutting speed: 230 n/min

[0055] feed rate: 0.3 mm/rev

[0056] depth of cut: 2.0 mm

[0057] cutting coolant: chemicool SR −1

[0058] Then, the flank wear (vB) of each cutting tool in case that thelength of cut is 5 km was measured. The measured results were evaluatedas the tool life of the cutting tools in the cutting test The results ofthese cutting tests are also shown in TABLE 1.

[0059] Furthermore, as a comparative example 1, a sintered cermetmaterial was prepared using a starting raw material which had thecomposition ratio indicated in TABLE I with Si₃N₄ excluded. As acomparative example 2, a sintered cermet material was prepared using astarting raw material which had the composition ratio indicated in TABLE1 with CrxN excluded. As a comparative example 3, a sintered cermetmaterial was prepared using a starting raw material which had thecomposition ratio indicated in TABLE 1 with metal components excluded.Comparative examples 1, 2 and 3 were subjected to the cutting tests,similarly.

[0060] In addition, as a conventional example 1, the cutting tool on themarket, which was composed of a conventional TiN—TiC—WC—Co sinteredcermet material, was subjected to the cutting test, similarly. As aconventional example 2, the cutting tool on the market which wascomposed of a conventional TiCN—WC—Co—VC—MoC sintered cermet material,was subjected to the cutting test, similarly. As conventional examples 3and 4, cutting tools on the market, which were composed of aconventional cBN sintered material, were subjected to the cutting testssimilarly. Conventional example 3 is a cutting tool composed of asintered material which was obtained by sintering a mixture material inwhich 80 vol. % of cBN and 20 vol. % of (WC—Co) were mixed. Conventionalexample 4 is a cutting tool composed of a sintered material which wasobtained by sintering a mixture material in which 60 vol. % of cBN and40 vol. % of (Al₂O₃—TiC) were mixed. The performance of each of theseconventional examples is also shown in TABLE 1.

[0061] As is apparent from TABLE 1, in No. 1 to No. 9 which correspondto embodiments of the present invention, the wear amount of each cuttingtool was small there was not observed any fracture therein, and the wearresistance and frame resistance thereof were good. Thus, the results ofthe cutting tests were good. In particular, where the starting rawmaterials contain SiC, the wear amounts of the resultant cutting toolswere small, there was not observed any fracture therein, and the wearresistance and fracture resistance thereof were good. Thus, the resultsof the cutting test were good.

[0062] In addition, as is apparent from TABLE 1, in No. 1 to No. 9 whichcorrespond to embodiments of the present invention, the wear amount ofthe resultant cutting tools decreased as the pressure upon stingincreased.

[0063] In comparative examples 1 to 3, the results of the cutting teststhereof were not good In particular, in the comparative example 2 whichdoes not contain CrN, the fracture occurred in the cutting tool,although the pressure upon sintering was as large as 30 MPa. In theconventional examples 1 to 4, the results of the cutting tests thereofwere not good. These results are estimated to be caused by CrN being notcontained

[0064] Si₃N₄ and SiC may be added in the form of whisker instead of theform of fine particulates. In the cutting tools of the embodiments,niresit cast iron was adopted as the material of work pieces, andniresit cast iron was cut. The present invention can be also applied tothe work pieces composed of other materials such as austemperedspheroidal graphite cast iron, normal cast iron including spheroidalgraphite cast iron and flake graphite cast iron, carbon steel and alloysteel.

[0065] The above-described embodiments are preferably used as the aimingtools for high speed cutting which is performed at a high cutting speed,and heavy cutting which is performed with a large cutting amount percutting work. In addition, they are also applicable to, other cuttingmethods than the high speed cutting and heavy cutting. For example, theyare applicable to the cutting methods wherein the cutting speed orcutting amount are normal.

[0066] In the above described embodiments, the present invention wasapplied to the cutting tools. The present invention is also applicableto reference metals, anvils, die punches, excavation bits or the like.Instead of the compositions of the embodiments, two, three or four kindsof metals selected from the group consisting of Co, Ni, Ta and Mo can bealso combined. The upper limit and lower limit of each of powders ofTiCN, Si₃N₄, Al₂O₃, CrxN and ZrN, at least one powder of W and WC, andat least one metal powder selected from the group consisting of Co, Ni,Ta and Mo may be limited to those indicated in TABLE 1, if required. Inaddition, the present invention is not looted to the embodimentsdisclosed before and shown in the drawings, and can be modified withoutdeparting from the spirit and scope of the present invention.

[0067] From the above disclosure, the following technical idea can bealso obtained.

[0068] Non-cBN sintered cermet materials containing no cBN, each beingcomposed of a sintered body which is obtained by preparing a mixedpowder containing powders of TiCN, Si₃N₄, Al₂O₃, CrxN (x=1-2.7) and ZrN,at least one powder of W and WC, and at least one A metal powderselected from the group consisting of Co, Ni, Ta and Mo, and sinteringthe prepared mixed powder, and a method for producing such non-cBNsintered cermet materials.

[0069] In accordance with the present invention, the heat resistance ofthe sintered cermet material is enhanced, and accordingly, when used atelevated temperatures, the hardness and strength can be ensured.Consequently, in the environments where there occurs contacting withother members, such as upon cutting, good wear resistance and goodfracture resistance can be ensured, and accordingly it is favorable forimproving the durability and extending life time of the materials. Forthese reasons, where the present invention is applied to cutting tools,work pieces composed of high class cast iron such as niresist cast, ironand austempered spheroidal graphite cast iron, which are difficult to becut, can be favorably subjected to the high speed cutting and the heavycutting. In addition, where such high speed cutting and heavy cuttingare applied to the work pieces composed of such high class cast iron,long tool life of cutting tools can be effected.

What is claimed is:
 1. A sintered cermet material for tools comprising:a sintered body which is obtained by preparing a powder mixturecomprising powders of TiCN, Si₃N₄, Al₂O3, CrxN (x=1-2.7) and ZrN, eitheror both of W and WC, and at least one metal selected from the groupconsisting of Co, Ni, Ta and Mo, and then sintering said powder mixture.2. The sintered cermet material as claimed in claim 1, wherein saidmixed powder comprises 1 to 20 vol. % of TiCN, relative to the volume ofoverall powders combined 1 to 10 vol. % of Si₃N₄, 1 to 20 vol. % ofAl₂O₃, 5 to 15 vol. % of CrxN (x=1-2.7) and 5 to 15 vol. % of ZrN suchthat the combined volume of powders of TiCN, Si₃N₄, Al₂O₃, CrxN and ZrNis between 13 to 70 vol. %, said mixed powder further comprising 20 to70,vol. % of either one or both of W and WC combined, and 1 to 20 vol. %of at least one metal powder selected from the group consisting of Co,Ni, Ta and Mo.
 3. The sintered cermet material as claimed in claim 1,wherein said mixed powder comprises 5 to 20 vol. % of SiC with externaladdition.
 4. The sintered cermet material as claimed in claim 1, whereinthe ratio in number of atoms of N and C in TiCN is between (1:9) and(9:1).
 5. The sintered cermet material as claimed in claim 1, whereinsaid mixed powder comprises 5 to 20 vol. % of TiCN.
 6. The sinteredcermet material as chimed in claim 1, wherein said TiCN powder has aparticle size of 5 μm or less.
 7. A sintered cermet material as claimedin claim 1, wherein where the total of said mixed powder is 100 vol. %,said mixed powder comprises 5 to 10 vol. % of Si₃N₄.
 8. The sinteredcermet material as claimed in claim 1, wherein said Si₃N₄ powder has aparticle size of 5 μm or less.
 9. The sintered cermet material asclaimed in claim 1, wherein said mixed powder comprises 5 to 20 vol. %of A₂O₃.
 10. The sintered cermet material as claimed in claim 1, whereinsaid Al₂O₃ powder has a particle size of 5 μm or less.
 11. The sinteredcermet material as claimed in claim 1, wherein sad mixed powdercomprises 8 to 13 vol. % of CrxN (x=1-2.7).
 12. The sintered cermetmaterial as claimed in claim 1, wherein said CrxN (x=1-2.7) powder has aparticle size of 5 μm or less.
 13. The sintered cermet material asclaimed in claim 1, wherein said mixed powder comprises 8 to 13 vol. %of ZrN.
 14. A sintered cermet material as claimed in claim 1, whereinsaid ZrN powder has a particle size of 5 μm or less.
 15. The sinteredcermet material as claimed in claim 1, wherein said mixed powdercomprises 30 to 60 vol. % of powder of either or both of W and WC. 16.The sintered cermet material as claimed in claim 1, wherein sad W and WCpowders have a particle size of 1 μm or less.
 17. The sintered cermetmaterial as claimed in claim 1, wherein said mixed powder comprises 5 to15 vol. % of at least one selected from the group consisting of Co, Ni,Ta and Mo.
 18. The sintered cermet material as claimed in claim 1,wherein said sintered cermet material is used in either cutting tools,reference metals, anvils, die punches or excavation bits.
 19. A methodfor producing a sintered cermet material comprising the steps ofpreparing a mixed powder containing powders of TiCN, Si₃N₄, Al₂O₃, CrxN(x=1-2.7) and ZrN, either or both of W and WC, and at least one metalselected from the group consisting of Co, Ni, Ta and Mo; and winteringsaid prepared mixed powder to produce a sintered body.
 20. The method asclaimed in claim 19, wherein wherein said mixed powder comprises 1 to 20vol. % of TiCN, 1 to 10 vol. % of Si₃N₄ 1 to 20 vol. % of Al₂O₃, 5 to 15vol. % of CrxN (x=1-2.7) and 5 to 15 vol. % of ZrN such that thecombined volume of powders of TiCN, Si₃N₄, Al₂O₃, CrxN and ZrN isbetween 13 and 70 vol. %, said mixed powder further comprises 20 to 70vol. % of either or both of W and WC combined, and 1 to 20 vol. % of atleast one kind of metal selected from the group consisting of Co, Ni, Taand Mo.
 21. The method as claimed in claim 19, wherein said mixed powdercontains 5 to 20 vol. % of SiC with external addition.
 22. The method asclaimed in claim 19, wherein said SiC has a particle size of 3 μm orless.
 23. The method as claimed in claim 19, wherein said step ofsintering is conducted at a temperature of 1300° to 1650° C.
 24. Themethod as claimed in claim 19, wherein said step of sintering isconducted at a pressure of 0.1 NPa to 2000 MNa and a temperature of1300° to 1650° C.
 25. The method as claimed in claim 19, wherein saidstep of sintering is conducted at a pressure of 0.1 MPa to 3000 MPa at atemperature of 1400° to 1550° C. for 0.5 to 6 hours.